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Tobias Wang - One of the best experts on this subject based on the ideXlab platform.

  • Weighing the evidence for using vascular conductance, not resistance, in comparative cardiovascular physiology.
    The Journal of Experimental Biology, 2019
    Co-Authors: William Joyce, Daniel W. White, Peter B. Raven, Tobias Wang
    Abstract:

    ABSTRACT Vascular resistance and conductance are reciprocal indices of vascular tone that are often assumed to be interchangeable. However, in most animals in vivo , blood flow (i.e. Cardiac output) typically varies much more than arterial blood pressure. When blood flow changes at a constant pressure, the relationship between conductance and blood flow is linear, whereas the relationship between resistance and blood flow is non-linear. Thus, for a given change in blood flow, the change in resistance depends on the starting point, whereas the attendant change in conductance is proportional to the change in blood flow regardless of the starting conditions. By comparing the effects of physical activity at different temperatures or between species – concepts at the heart of comparative cardiovascular physiology – we demonstrate that the difference between choosing resistance or conductance can be marked. We also explain here how the ratio of conductance in the pulmonary and systemic circulations provides a more intuitive description of Cardiac Shunt patterns in the reptilian cardiovascular system than the more commonly used ratio of resistance. Finally, we posit that, although the decision to use conductance or resistance should be made on a case-by-case basis, in most circumstances, conductance is a more faithful portrayal of cardiovascular regulation in vertebrates.

  • deciphering function of the pulmonary arterial sphincters in loggerhead sea turtles caretta caretta
    The Journal of Experimental Biology, 2018
    Co-Authors: Daniel Garciaparraga, Tobias Wang, Teresa Lorenzo, Jose Luis Ortiz, J Ortega, Jose Luis Crespopicazo, Julio Cortijo, Andreas Fahlman
    Abstract:

    ABSTRACT To provide new insight into the pathophysiological mechanisms underlying gas emboli (GE) in bycaught loggerhead sea turtles (Caretta caretta), we investigated the vasoactive characteristics of the pulmonary and systemic arteries, and the lung parenchyma (LP). Tissues were opportunistically excised from recently dead animals for in vitro studies of vasoactive responses to four different neurotransmitters: acetylcholine (ACh; parasympathetic), serotonin (5HT), adrenaline (Adr; sympathetic) and histamine. The significant amount of smooth muscle in the LP contracted in response to ACh, Adr and histamine. The intrapulmonary and systemic arteries contracted under both parasympathetic and sympathetic stimulation and when exposed to 5HT. However, proximal extrapulmonary arterial (PEPA) sections contracted in response to ACh and 5HT, whereas Adr caused relaxation. In sea turtles, the relaxation in the pulmonary artery was particularly pronounced at the level of the pulmonary artery sphincter (PASp), where the vessel wall was highly muscular. For comparison, we also studied tissue response in freshwater sliders turtles (Trachemys scripta elegans). Both PEPA and LP from freshwater sliders contracted in response to 5HT, ACh and also Adr. We propose that in sea turtles, the dive response (parasympathetic tone) constricts the PEPA, LP and PASp, causing a pulmonary Shunt and limiting gas uptake at depth, which reduces the risk of GE during long and deep dives. Elevated sympathetic tone caused by forced submersion during entanglement with fishing gear increases the pulmonary blood flow causing an increase in N2 uptake, potentially leading to the formation of blood and tissue GE at the surface. These findings provide potential physiological and anatomical explanations on how these animals have evolved a Cardiac Shunt pattern that regulates gas exchange during deep and prolonged diving.

  • vagal tone regulates Cardiac Shunts during activity and at low temperatures in the south american rattlesnake crotalus durissus
    Journal of Comparative Physiology B-biochemical Systemic and Environmental Physiology, 2016
    Co-Authors: Renato Filogonio, Tobias Wang, E W Taylor, Augusto Shinya Abe, Cleo A C Leite
    Abstract:

    The undivided ventricle of non-crocodilian reptiles allows for intraCardiac admixture of oxygen-poor and oxygen-rich blood returning via the atria from the systemic circuit and the lungs. The distribution of blood flow between the systemic and pulmonary circuits may vary, based on differences between systemic and pulmonary vascular conductances. The South American rattlesnake, Crotalus durissus, has a single pulmonary artery, innervated by the left vagus. Activity in this nerve controls pulmonary conductance so that left vagotomy abolishes this control. Experimental left vagotomy to abolish Cardiac Shunting had no effect on long-term survival and failed to identify a functional role in determining metabolic rate, growth or resistance to food deprivation. Accordingly, the present investigation sought to evaluate the extent to which Cardiac Shunt patterns are actively controlled during changes in body temperature and activity levels. We compared hemodynamic parameters between intact and left-vagotomized rattlesnakes held at different temperatures and subjected to enforced physical activity. Increased temperature and enforced activity raised heart rate, Cardiac output, pulmonary and systemic blood flow in both groups, but net Cardiac Shunt was reversed in the vagotomized group at lower temperatures. We conclude that vagal control of pulmonary conductance is an active mechanism regulating Cardiac Shunts in C. durissus.

  • ablation of the ability to control the right to left Cardiac Shunt does not affect oxygen uptake specific dynamic action or growth in the rattlesnake crotalus durissus
    The Journal of Experimental Biology, 2013
    Co-Authors: Tobias Wang, Cleo A C Leite, E W Taylor, Augusto Shinya Abe, Denis V Andrade
    Abstract:

    The morphologically undivided ventricle of the heart in non-crocodilian reptiles permits the mixing of oxygen-rich blood returning from the lungs and oxygen-poor blood from the systemic circulation. A possible functional significance for this intra-Cardiac Shunt has been debated for almost a century. Unilateral left vagotomy rendered the single effective pulmonary artery of the South American rattlesnake, Crotalus durissus , unable to adjust the magnitude of blood flow to the lung. The higher constant perfusion of the lung circulation and the incapability of adjusting the right–left Shunt in left-denervated snakes persisted over time, providing a unique model for investigation of the long-term consequences of Cardiac Shunting in a squamate. Oxygen uptake recorded at rest and during spontaneous and forced activity was not affected by removing control of the Cardiac Shunt. Furthermore, metabolic rate and energetic balance during the post-prandial metabolic increment, plus the food conversion efficiency and growth rate, were all similarly unaffected. These results show that control of Cardiac Shunting is not associated with a clear functional advantage in adjusting metabolic rate, effectiveness of digestion or growth rates.

  • Local control of pulmonary blood flow and lung structure in reptiles: implications for ventilation perfusion matching.
    Respiratory Physiology & Neurobiology, 2006
    Co-Authors: Nini Skovgaard, Tobias Wang
    Abstract:

    Abstract Lung structure of reptiles is very diverse ranging from single chambered lungs with a simple structure to more complex and multi-chambered lungs. Increased structural complexity resulted from the evolution of smaller gas exchange units and larger surface area, which increases the pulmonary diffusive capacity for O2. However, increased structural complexity probably also increases the possibilities for ventilation–perfusion ( V ˙ / Q ˙ ) heterogeneity, which exerts significant constraints on gas exchange. In most reptiles, the ventricle is anatomically and functionally undivided so blood pressures are equal in the systemic and pulmonary circulations. In these species, blood flow distribution between pulmonary and systemic circulations are primarily determined by pulmonary and systemic vascular resistances. Thus, increased pulmonary resistance lowers pulmonary blood flow through increasing Cardiac right-to-left Shunt decreasing systemic oxygen levels. It has been proposed that local mechanisms regulating pulmonary blood flow are more pronounced in reptiles with complex lungs as they are more prone to V ˙ / Q ˙ heterogeneity. However, local control of pulmonary blood flow has also been suggested to primarily exist when hearts are functionally divided because altered pulmonary vascular resistance does not affect Cardiac Shunt patterns. Data suggest that, while there seems to be a general trend of increased local regulation of pulmonary blood flow in species with structurally complex lungs and divided hearts, it is also possible that other factors, such as breathing pattern, have been important for the evolutionary development of local regulatory mechanisms in the lungs.

Cleo A C Leite - One of the best experts on this subject based on the ideXlab platform.

  • vagal tone regulates Cardiac Shunts during activity and at low temperatures in the south american rattlesnake crotalus durissus
    Journal of Comparative Physiology B-biochemical Systemic and Environmental Physiology, 2016
    Co-Authors: Renato Filogonio, Tobias Wang, E W Taylor, Augusto Shinya Abe, Cleo A C Leite
    Abstract:

    The undivided ventricle of non-crocodilian reptiles allows for intraCardiac admixture of oxygen-poor and oxygen-rich blood returning via the atria from the systemic circuit and the lungs. The distribution of blood flow between the systemic and pulmonary circuits may vary, based on differences between systemic and pulmonary vascular conductances. The South American rattlesnake, Crotalus durissus, has a single pulmonary artery, innervated by the left vagus. Activity in this nerve controls pulmonary conductance so that left vagotomy abolishes this control. Experimental left vagotomy to abolish Cardiac Shunting had no effect on long-term survival and failed to identify a functional role in determining metabolic rate, growth or resistance to food deprivation. Accordingly, the present investigation sought to evaluate the extent to which Cardiac Shunt patterns are actively controlled during changes in body temperature and activity levels. We compared hemodynamic parameters between intact and left-vagotomized rattlesnakes held at different temperatures and subjected to enforced physical activity. Increased temperature and enforced activity raised heart rate, Cardiac output, pulmonary and systemic blood flow in both groups, but net Cardiac Shunt was reversed in the vagotomized group at lower temperatures. We conclude that vagal control of pulmonary conductance is an active mechanism regulating Cardiac Shunts in C. durissus.

  • ablation of the ability to control the right to left Cardiac Shunt does not affect oxygen uptake specific dynamic action or growth in the rattlesnake crotalus durissus
    The Journal of Experimental Biology, 2013
    Co-Authors: Tobias Wang, Cleo A C Leite, E W Taylor, Augusto Shinya Abe, Denis V Andrade
    Abstract:

    The morphologically undivided ventricle of the heart in non-crocodilian reptiles permits the mixing of oxygen-rich blood returning from the lungs and oxygen-poor blood from the systemic circulation. A possible functional significance for this intra-Cardiac Shunt has been debated for almost a century. Unilateral left vagotomy rendered the single effective pulmonary artery of the South American rattlesnake, Crotalus durissus , unable to adjust the magnitude of blood flow to the lung. The higher constant perfusion of the lung circulation and the incapability of adjusting the right–left Shunt in left-denervated snakes persisted over time, providing a unique model for investigation of the long-term consequences of Cardiac Shunting in a squamate. Oxygen uptake recorded at rest and during spontaneous and forced activity was not affected by removing control of the Cardiac Shunt. Furthermore, metabolic rate and energetic balance during the post-prandial metabolic increment, plus the food conversion efficiency and growth rate, were all similarly unaffected. These results show that control of Cardiac Shunting is not associated with a clear functional advantage in adjusting metabolic rate, effectiveness of digestion or growth rates.

James Hicks - One of the best experts on this subject based on the ideXlab platform.

  • surgical removal of right to left Cardiac Shunt in the american alligator alligator mississippiensis causes ventricular enlargement but does not alter apnoea or metabolism during diving
    The Journal of Experimental Biology, 2009
    Co-Authors: John Eme, June Gwalthney, Tomasz Owerkowicz, Jason M Blank, Gildardo Barron, James Hicks
    Abstract:

    Crocodilians have complete anatomical separation between the ventricles, similar to birds and mammals, but retain the dual aortic arch system found in all non-avian reptiles. This Cardiac anatomy allows surgical modification that prevents right-to-left (R-L) Cardiac Shunt. A R-L Shunt is a bypass of the pulmonary circulation and recirculation of oxygen-poor blood back to the systemic circulation and has often been observed during the frequent apnoeic periods of non-avian reptiles, particularly during diving in aquatic species. We eliminated R-L Shunt in American alligators (Alligator mississippiensis) by surgically occluding the left aorta (LAo; arising from right ventricle) upstream and downstream of the foramen of Panizza (FoP), and we tested the hypotheses that this removal of R-L Shunt would cause afterload-induced Cardiac remodelling and adversely affect diving performance. Occlusion of the LAo both upstream and downstream of the FoP for approximately 21 months caused a doubling of RV pressure and significant ventricular enlargement (average approximately 65%) compared with age-matched, sham-operated animals. In a separate group of recovered, surgically altered alligators allowed to dive freely in a dive chamber at 23 degrees C, occlusion of the LAo did not alter oxygen consumption or voluntary apnoeic periods relative to sham animals. While surgical removal of R-L Shunt causes considerable changes in Cardiac morphology similar to aortic banding in mammals, its removal does not affect the respiratory pattern or metabolism of alligators. It appears probable that the low metabolic rate of reptiles, rather than pulmonary circulatory bypass, allows for normal aerobic dives.

  • Cardiac output and Shunt during voluntary activity at different temperatures in the turtle trachemys scripta
    Physiological and Biochemical Zoology, 2003
    Co-Authors: Egle Krosniunas, James Hicks
    Abstract:

    Red-eared slider turtles (Trachemys scripta) were chronically instrumented with blood flow probes for a long-term study of voluntary behavior in an enriched laboratory setting. Cardiovascular measures consisting of total Cardiac output (Q(tot)), pulmonary blood flow (Q(pul)), systemic blood flow (Q(sys)), net Cardiac Shunt (Q(Shunt)), heart rate (HR), and stroke volume (SV) were obtained during spontaneous activity at a constant body temperature (Tb=2 degrees C) and at unstable (variable) T(b)'s ranging from 19 degrees to 37 degrees C. The effects of temperature and activity differed between the pulmonary and systemic circuits, with increases in Q(sys) due to HR alone, while both HR and SV contributed to gains in Q(pul). At stable 20 degrees C, cardiovascular responses during diving, submerged swimming, and walking were qualitatively similar, and increases in Q(tot) during activity ( approximately 2 x resting levels) were due to greater gains in Q(pul) than Q(sys). At unstable T(b)'s and in general, net Q(Shunt) while active depended on the integration of individual physiological influences such as heating, cooling, and initial behavioral state acting on the cardiovascular system. During activity, net left-to-right (L-R) Shunts predominated at constant T(b) of 20 degrees C (mean Shunt fraction approximately 30%-40%), while both net L-R and right-to-left (R-L) Shunts of varying size were found at unstable T(b)'s (19 degrees - 37 degrees C).

James W Hicks - One of the best experts on this subject based on the ideXlab platform.

  • turning crocodilian hearts into bird hearts growth rates are similar for alligators with and without right to left Cardiac Shunt
    The Journal of Experimental Biology, 2010
    Co-Authors: John Eme, June Gwalthney, Tomasz Owerkowicz, Jason M Blank, James W Hicks
    Abstract:

    The functional and possible adaptive significance of non-avian reptiles' dual aortic arch system and the ability of all non-avian reptiles to perform central vascular Cardiac Shunts have been of great interest to comparative physiologists. The unique Cardiac anatomy of crocodilians - a four-chambered heart with the dual aortic arch system - allows for only right-to-left (R-L; pulmonary bypass) Cardiac Shunt and for surgical elimination of this Shunt. Surgical removal of the R-L Shunt, by occluding the left aorta (LAo) upstream and downstream of the foramen of Panizza, results in a crocodilian with an obligatory, avian/mammalian central circulation. In this study, R-L Cardiac Shunt was eliminated in age-matched, female American alligators (Alligator mississippiensis; 5-7 months of age). We tested the hypothesis that surgical elimination of R-L Cardiac Shunt would impair growth (a readily measured proxy for fitness) compared with sham-operated, age-matched controls, especially in animals subjected to exhaustive exercise. While regular exercise caused a decrease in size (snout-to-vent length, head length and body mass), elimination of the capacity for R-L Cardiac Shunt did not greatly reduce animal growth, despite a chronic ventricular enlargement in surgically altered juvenile alligators. We speculate that, despite being slightly smaller, alligators with an occluded LAo would have reached sexual maturity in the same breeding season as control alligators. This study suggests that crocodilian R-L Cardiac Shunt does not provide an adaptive advantage for juvenile alligator growth and supports the logic that Cardiac Shunts persist in crocodilians because they have not been selected against.

  • surgical removal of right to left Cardiac Shunt in the american alligator alligator mississippiensis causes ventricular enlargement but does not alter apnoea or metabolism during diving
    The Journal of Experimental Biology, 2009
    Co-Authors: June Gwalthney, Tomasz Owerkowicz, Jason M Blank, Gildardo Barron, James W Hicks
    Abstract:

    SUMMARY Crocodilians have complete anatomical separation between the ventricles, similar to birds and mammals, but retain the dual aortic arch system found in all non-avian reptiles. This Cardiac anatomy allows surgical modification that prevents right-to-left (R–L) Cardiac Shunt. A R–L Shunt is a bypass of the pulmonary circulation and recirculation of oxygen-poor blood back to the systemic circulation and has often been observed during the frequent apnoeic periods of non-avian reptiles, particularly during diving in aquatic species. We eliminated R–L Shunt in American alligators ( Alligator mississippiensis ) by surgically occluding the left aorta (LAo; arising from right ventricle) upstream and downstream of the foramen of Panizza (FoP), and we tested the hypotheses that this removal of R–L Shunt would cause afterload-induced Cardiac remodelling and adversely affect diving performance. Occlusion of the LAo both upstream and downstream of the FoP for ∼21 months caused a doubling of RV pressure and significant ventricular enlargement (average ∼65%) compared with age-matched, sham-operated animals. In a separate group of recovered, surgically altered alligators allowed to dive freely in a dive chamber at 23°C, occlusion of the LAo did not alter oxygen consumption or voluntary apnoeic periods relative to sham animals. While surgical removal of R–L Shunt causes considerable changes in Cardiac morphology similar to aortic banding in mammals, its removal does not affect the respiratory pattern or metabolism of alligators. It appears probable that the low metabolic rate of reptiles, rather than pulmonary circulatory bypass, allows for normal aerobic dives.

June Gwalthney - One of the best experts on this subject based on the ideXlab platform.

  • turning crocodilian hearts into bird hearts growth rates are similar for alligators with and without right to left Cardiac Shunt
    The Journal of Experimental Biology, 2010
    Co-Authors: John Eme, June Gwalthney, Tomasz Owerkowicz, Jason M Blank, James W Hicks
    Abstract:

    The functional and possible adaptive significance of non-avian reptiles' dual aortic arch system and the ability of all non-avian reptiles to perform central vascular Cardiac Shunts have been of great interest to comparative physiologists. The unique Cardiac anatomy of crocodilians - a four-chambered heart with the dual aortic arch system - allows for only right-to-left (R-L; pulmonary bypass) Cardiac Shunt and for surgical elimination of this Shunt. Surgical removal of the R-L Shunt, by occluding the left aorta (LAo) upstream and downstream of the foramen of Panizza, results in a crocodilian with an obligatory, avian/mammalian central circulation. In this study, R-L Cardiac Shunt was eliminated in age-matched, female American alligators (Alligator mississippiensis; 5-7 months of age). We tested the hypothesis that surgical elimination of R-L Cardiac Shunt would impair growth (a readily measured proxy for fitness) compared with sham-operated, age-matched controls, especially in animals subjected to exhaustive exercise. While regular exercise caused a decrease in size (snout-to-vent length, head length and body mass), elimination of the capacity for R-L Cardiac Shunt did not greatly reduce animal growth, despite a chronic ventricular enlargement in surgically altered juvenile alligators. We speculate that, despite being slightly smaller, alligators with an occluded LAo would have reached sexual maturity in the same breeding season as control alligators. This study suggests that crocodilian R-L Cardiac Shunt does not provide an adaptive advantage for juvenile alligator growth and supports the logic that Cardiac Shunts persist in crocodilians because they have not been selected against.

  • surgical removal of right to left Cardiac Shunt in the american alligator alligator mississippiensis causes ventricular enlargement but does not alter apnoea or metabolism during diving
    The Journal of Experimental Biology, 2009
    Co-Authors: June Gwalthney, Tomasz Owerkowicz, Jason M Blank, Gildardo Barron, James W Hicks
    Abstract:

    SUMMARY Crocodilians have complete anatomical separation between the ventricles, similar to birds and mammals, but retain the dual aortic arch system found in all non-avian reptiles. This Cardiac anatomy allows surgical modification that prevents right-to-left (R–L) Cardiac Shunt. A R–L Shunt is a bypass of the pulmonary circulation and recirculation of oxygen-poor blood back to the systemic circulation and has often been observed during the frequent apnoeic periods of non-avian reptiles, particularly during diving in aquatic species. We eliminated R–L Shunt in American alligators ( Alligator mississippiensis ) by surgically occluding the left aorta (LAo; arising from right ventricle) upstream and downstream of the foramen of Panizza (FoP), and we tested the hypotheses that this removal of R–L Shunt would cause afterload-induced Cardiac remodelling and adversely affect diving performance. Occlusion of the LAo both upstream and downstream of the FoP for ∼21 months caused a doubling of RV pressure and significant ventricular enlargement (average ∼65%) compared with age-matched, sham-operated animals. In a separate group of recovered, surgically altered alligators allowed to dive freely in a dive chamber at 23°C, occlusion of the LAo did not alter oxygen consumption or voluntary apnoeic periods relative to sham animals. While surgical removal of R–L Shunt causes considerable changes in Cardiac morphology similar to aortic banding in mammals, its removal does not affect the respiratory pattern or metabolism of alligators. It appears probable that the low metabolic rate of reptiles, rather than pulmonary circulatory bypass, allows for normal aerobic dives.

  • surgical removal of right to left Cardiac Shunt in the american alligator alligator mississippiensis causes ventricular enlargement but does not alter apnoea or metabolism during diving
    The Journal of Experimental Biology, 2009
    Co-Authors: John Eme, June Gwalthney, Tomasz Owerkowicz, Jason M Blank, Gildardo Barron, James Hicks
    Abstract:

    Crocodilians have complete anatomical separation between the ventricles, similar to birds and mammals, but retain the dual aortic arch system found in all non-avian reptiles. This Cardiac anatomy allows surgical modification that prevents right-to-left (R-L) Cardiac Shunt. A R-L Shunt is a bypass of the pulmonary circulation and recirculation of oxygen-poor blood back to the systemic circulation and has often been observed during the frequent apnoeic periods of non-avian reptiles, particularly during diving in aquatic species. We eliminated R-L Shunt in American alligators (Alligator mississippiensis) by surgically occluding the left aorta (LAo; arising from right ventricle) upstream and downstream of the foramen of Panizza (FoP), and we tested the hypotheses that this removal of R-L Shunt would cause afterload-induced Cardiac remodelling and adversely affect diving performance. Occlusion of the LAo both upstream and downstream of the FoP for approximately 21 months caused a doubling of RV pressure and significant ventricular enlargement (average approximately 65%) compared with age-matched, sham-operated animals. In a separate group of recovered, surgically altered alligators allowed to dive freely in a dive chamber at 23 degrees C, occlusion of the LAo did not alter oxygen consumption or voluntary apnoeic periods relative to sham animals. While surgical removal of R-L Shunt causes considerable changes in Cardiac morphology similar to aortic banding in mammals, its removal does not affect the respiratory pattern or metabolism of alligators. It appears probable that the low metabolic rate of reptiles, rather than pulmonary circulatory bypass, allows for normal aerobic dives.